The Collaborative International Dictionary of English v.0.48:

Resuscitator \Re*sus"ci*ta`tor\, n. [L.]
   1. One who, or that which, resuscitates.
      [1913 Webster]

   2. Specifically: (Med.) A device which is used to force
      oxygen or a mixture of oxygen and other gases into the
      lungs of patients who are suffering from asphyxiation, to
      revive the patient and induce resumption of respiration.
      [PJC]

WordNet (r) 3.0 (2006):

resuscitator
    n 1: a breathing apparatus used for resuscitation by forcing
         oxygen into the lungs of a person who has undergone
         asphyxia or arrest of respiration